Infrared landing system for aircraft



July 5, 1960. T. R. WHITNEY ETA!- INFRARED LANDING SYSTEM FOR AIRCRAFT 4 Sheets-Sheet 1 Filed Feb. 1, 1955 INVENTORS. THEODORE R. WHITNEY BY AVARD F. FAIRBANKS www ATTORNEY uly 1960 T. R. WHlTNEY ETAL I 2,944,151

INFRARED LANDING SYSTEM FOR AIRCRAFT Filed Feb. 1, 1955 4 SheetsSheet 2 AIMING LEFT AIMING HIGH AIMING RIGHT M FIG. 4 FIG. 5

I0 Io FLYING Too FAR LEFT 0N PATH FLYING Too FAR RIGHT FIG. 6 FIG. 7 FIG. 8

FLYING HIGH AIMING LOW FLYING LOW FIG. 9 FIG. IO FIG. ll

INVENTORS. THEODORE R. WHITNEY By AVARD F. FAlRBANKS ATTORNEY July 5, 1960 T. R. WHITNEY ET AL 2,944,151

INFRARED LANDING SYSTEM FOR AIRCRAFT Filed Feb. 1, 1955 4 Sheets-Sheet 3 X MAX.

INVENTORJ. THEO E R. WHITNEY AVAR FAIRBANKS ATTORNEY July 5, 19 0 "r. R. WHITNEY ET 2,944,151

INFRARED LANDING SYSTEM FOR AIRCRAFT Filed Feb. 1, 1955 4 Sheets-Sheet 4 FIG. l3 INVENTORS- THEODORE R. WHITNEY BY AVARD F. FAIRBANKS ATTORNEY INFRARED LANDING SYSTEMFOR AIRCRAFT Theodore R. Whitney, Whittier, and AvardJ. Fairbanks, South San Gabriel, Calif. ,.assignors to North American Aviation, Inc. I

FiledFeb. 1, 1955, Ser. No. 485,381 'S'Claims. (Cl. 250-833) This invention pertains to a landing system foraircraft region of the electromagnetic spectrum; Radiation of:

this wave length would enable maintaining, an airportin complete blackout, yet would aiford beacons to allow safe landing of aircraft. In addition, infrared-sensitive devices provide a high degree of angular resolution, furnishing accurate information as to runway approach bearings.,-

Anliniber of. infrared radiatingbeacons are located to delineate a runway strip and are directed'sothat several beacons may be viewed on an indicator in the aircraft by the pilot, providing himseveral elements of information, suchas correct aim, correct altitude, correct lateral position and distance to the runway.

It is therefore an object of thisinvention to provide an infrared landing system for aircraft. It is another object of thisinvention to provide an invisible, high resolution beacon for landing aircraft.

It is another object of this invention to provide an in.- frared landing system which indicates to the pilot, of an aircraftthe proper glide path, heading, altitude, and distance totouchdown. ,It is still another object of this invention. to provide an infrared landing system which indicateserrors inair craftaim, altitude, lateral position, in continuous and,

simultaneous display.

Other objects of theIinvention will become apparentfrom the following descripiton takenin connection with,

the accompanying. drawings, in which Fig, l'illustrates a landing field and ten beacons;

Fig. 2 is a plan view of thecoveragebyeach beacon;

Figs. 3, 4, 5, 6, 7, 8,9, 10, and-11 are various pictorial displaysof'thebeacons, indicating to the pilot necessary corrections of the flight path;

Fig. 12 is an illustration of a beacon;

Fig; 13 is an illustrationof ,a scanner;

Fig. 14 illustrates the spiral scan obtained;

Fig. 15 is an electrical schematic of a sweep circuit which synchronizes the oscilloscope with the scanner, and.

Fig. 16 is a diagram of the receiver system carried by theaircraft.

Referring now to Fig. 1, an airstrip 1 is delineated by beacons 3, 4, 5, and 6. Beacons 7 and Sare disposed off the near end of the runway... Eachof these beacons is indicated as'radiating in vertical-sectors having an elevation coverage to sixty degrees. These sectors converge. Bea- Patented. July 5, 1 96 con '7 indicates that each beacon has a horizontal angular coverage of ten degrees left of line 9 *(awaiyfrom the airstrip). Line 9 is parallel to the runway. The fields of coverage of beacons and 6 are similar to that of beacon 7. The fields of coverage ofbeacons -3, 4, and Sara similarly ten degrees away. from strip 1 and-two degrees toward strip '1. Each beacon radiates in a given ;sector and all sectors overlap to define a common areawhich is thecorrect'approach to the runway. Beacons 2 and radiate in overlapping horizontal sectors to indicate the glide path, and their respective fieldsof coverage are as indicated. These beacons laterally definethe approach path to the runway. Beacons 11 and 12 are distance beacons and provide indications to the pilot ofdistance" .to go to touchdown.

Fig. 2- is a planview of theradiating fields of each of the beaconsshowing the angular coverage. Eachbeacon.

transmits in a given sector, which sectorsoverlap to define a correct glide path. v

Assuming that the view is reproduced and presented visually to the pilot on an oscilloscope, the various indications for correct and 'incorrect'landjng flight path would? be those indicated in Fig. 3'and followihg. In 3 for example, beacons 2-, 3, 4, 5, 6, 7, 8 and 10 appear on the; right side of 'the face ofthe oscilloscope and indicate the pilotis aiming too far to the left; Inasmucnas all beacons are visible, the lateral position and altitude are correct.' Fig. 4, in whichbeacons 3,4,5, and 6 only are visible indicates that the pilot is aiming too high. Fig. 5

indicates that the pilot'is aiming too far to the right. Fig.

6 indicates that the pilot is too-far to ithe lef-tlaterallyQ but aiming generally in the correct direction withrespect.- to the field. This illustrates thereascn for havingthe,

beacons visible for a greater angle awayv from the'airport than toward the airport. Oneor more beacons then dis-. appear at incorrect approach positions. Fig. 7 illustrates a correct approach. Fig. 8 illustrates flyingtoo far to the right. Fig. 9 illustrates, a position which is too, high. Beacon 10 is not visible. Fig. 10 illustrates an which is too low. Fig. 11 illustrates a position which. is too low. Beacon 2 is not visible. It will be noticed that the central location on the indicator of all or, most of the; beacons indicates a correctaim. The. disaPP- arance off one or more beacons indicates an incorrect altitude, or,

lateral position. The preceding figures do not include;

a presentation of distance beacons ,ll and 12 of Fig.1,

Fig. 12 is a beacon and indicates a practical construction. Power is received through cable14 at a. base 15; in which may be included transformers and rectificrs. foreach beacon. An ordinary tungsten projectionbulb pro-,

vides suitable radiation and is illustrated bybulb 16, 10;. Infrared-transmitting. lenses 18 and 19,. of fused quartz, act to re-imagethe. source in theplane ofchopperdisc 20 having radial, slits, The light is modulated at 10,000 cycles per second by, the, slits of chopperdisc 20 which, is driventhrough gear cated in front of reflector; ,17.

train 21 by motor 22., Motor 22. alsodrives a blower which acts tocool the'tungsten bulb 16. Reflector 17 is located immediately behind the light source and images;

the filaments within the lamp slightly, displaced totheside, creating interlaced, inverted images between the sources. This is common practice in projector systems.

' Immediately in front of the mechanical chopper disc 20 is a germanium filter 51, which is a single crystal; about 0.1 inch thick having a coat of selenium to reduce surface;

reflection losses. This is followed by a' spherical, fusedquartz objective lens 52 and a fused-quartz cylindrical lens 23. The cylindrical lens provides the dispersion oflightillustratedinF-igs. 1 and 2. Each of these lenses;52;and'= 23 are adjustable in either direction for focusing tungsten bulb 16. The peak radiation of tungsten lamp 16 is at wave lengths near 1.5 microns. In addition to cylindrical lens 23, optical stop 24 may be used to provide for shaping the beam to radiate in the desired vertical or hori zontal sectors.

An infrared receiver is located on an airplane to view the beacons illustrated in Fig. 1 and may be provided to scan a field of view of degrees in diameter. Such a receiver is capable of providing angular indication down to one-half degree horizontally or vertically and'is able to detect a beacon described in Fig. 12 at a distance of up to five miles, depending on the strength of the beacon and the sensitivity of the infrared-sensitive detector. Fig. 13 illustrates the infrared receiver in which a spherical collector mirror (or scanner) is flexibly connected to shaft 26 through a ball mount 27 and wedge-shaped hub 28. Mirror 25 may be a paraboloid. The ball joint connection allows a nutating motion of mirror 25. Infrared-senstive cell 29, located in front of mirror 25 approximately at the focal point, is enclosed in shield 30 having an aperture 31 which is serrated to reduce reflections. Mirror 25 is adapted to nutate with respect to its rotating axis and when the mirror is spun the scanned image appears to travel in a circle at the same rate of speed. Bearings 36 and 37 mount gear train 34. A wedgeshaped cam 32 is driven through a differential 33 in the same direction at a slightly lower rate of speed than mir ror 25. For example, mirror 25 rotates at twenty revolutions per second and cam 32 rotates at nineteen revolutions per second. Gear train 34 drives both the differential 33 and the shaft 26 according to motor 35. Spider 33a and spider gears 33b and 330 are rotated by shaft 26. Gear train 34 rotates the input gear 33d at a speed of one revolution per second. Output gear 33e, therefore, rotates at a speed one revolution per second slower than shaft 26, namely, nineteen revolutions per second. This provides a circular scan which decreases in size or, in effect, a spiral pattern. Although the cell element 29 remains at the focal point of collector mirror 25 the image moves across it and the pattern of scan is easier to visualize if it is considered that the cell moves across the image. Once per cycle the cell 29 scans in a spiral from the outside of circular field twenty degrees in diameter down to the center and then out again, as illustrated in Fig. 14. As shaft 26 is rotated, two-phase generator 38 is also rotated to provide a two-phase, sinusoidal, quadrature voltage which may be applied to the oscilloscope deflection plates to obtain a deflection which corresponds with the sweep of the optical scanning device. For example, one phase would provide a sinusoidal voltage of Y max maximum amplitude for Y deflection and the other phase would provide a sinusoidal voltage of X max maximum amplitude for X deflection, as illustrated in Fig. 14. Inasmuch as these amplitudes decrease as the spiral gets smaller, the outputs of the twophase generator are first connected to two potentiometers (only potentiometer 39 is shown), which potentiometers are rotated by worm-gear 40 which is driven according to gear train 34 to provide an electrical output which decreases as the spiral decreases. That is, these potentiometers change Y max and X max to instantaneous values, to Y and X, shown in Fig. 14. The outputs of these potentiometers are then sent to deflection amplifiers 41 and 42.

Fig. 15' further illustrates the connections of two potentiometers 39 and 43 and two-phase generator 38. The constant amplitude, sine wave output of two-phase generator 38 is thus modified by the potentiometers to provide increasing and decreasing signals according to the spiral scan which are then sent to the deflection plates of the oscilloscope, which is illustrated in Fig. 16. In Fig. 1 6, infrared detector 44 is indicated as being directable vertically by a control knob 45 operated by the pilot, and indicator 46 indicates to the pilot the vertical aim.

The output of the infrared cell is first sent to clipper 48 to remove all noise and weak signals below a given level. A filter 49 having a pass-band at about 10,000 cycles, which is the chopped frequency of the beacon, receives the signal from the clipper and transmits it to amplifier 50 which provides the signal to the intensity grid of the indicator to generate a pip representing each beacon as detected by the infrared cell during the scan of the mirror.

In this manner, a number of beacons located at an air port are displayed in their spatial relationship on an indicator tube for the pilot. If the aircraft is in an incorrect flight location, certain of the beacons will be visible to him or appear in given position on the oscilloscope to indicate his incorrect flight position. It will be noted that no gradations of infrared intensity are involvedand the information is obtained from the location or the appearance or non-appearance of each beacon on the oscilloscope. Use of range beacons 11 and 12 may be obtained by an additional receiver, such as receiver 44 of Fig. 16. Such an additional receiver would also be connected to the intensity grid of the cathode ray tube of the oscilloscope, or a separate gun of a two-gun cathode ray tube, or in a separate indicator to indicate when the aircraft is directly over the range marker beacons.

Although the invention has'been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. In an infrared landing system for aircraft, a first plurality of infrared beacons radiating vertically in restricted sectors, a second plurality of infrared beacons radiating horizontally in restricted sectors, said vertically and horizontally radiating beacons overlapping to define a common area indicating a correct landing approach, an airborne infrared receiver comprising an infrared-sensitive element, a scanner in spaced relationship with said infrared sensitive element, an oscilloscope, and means for synchronizing the beam sweep of said oscilloscope with the sweep of said scanner and the intensity of said oscilloscope connected to be controlled by said infrared-sensitive element.

2. In an infrared landing system for aircraft having a landing area, a first plurality of infrared beacons positioned on said landing area to radiate vertically in restricted sectors, said sectors overlapping to define a glide path vertically, a second plurality of infrared beacons delineating said landing area and radiating horizontally in restricted sectors, said sectors overlapping to define laterally a glide path, all of said restricted sectors of said first and second plurality of infrared beacons overlapping to define a common area indicating a correct landing approach for said aircraft, and a third plurality of infrared beacons radiating in restricted sectors, said beacons radiating vertically in sectors perpendicular to said landing area to provide distance information.

3. The combination recited in claim 2 wherein is included an infrared receiver comprising an infrared-sensitive element, a scanner in spaced relationship with said infrared-sensitive element, means for providing a spiral motion of said scanner, and an oscilloscope and means for synchronizing the sweep of said oscilloscope with the sweep of said scanner, the intensity of said oscilloscope connected to be controlled by the output of the infraredsensitive element of said receiver.

4. In an infrared landing system for an aircraft, a plurality of infrared glide path beacons radiating in horizontal overlapping sectors, the common portion of said sectors defining a glide path, a plurality of runway marker infrared radiating beacons radiating in vertical, overlapping sectors, the common portion of said vertical sectors laterally defining said glide path, all of said sectors of 5 said beacons radiating overlapping to define a common area indicating a correct approach for said aircraft.

5. The combination recited in claim 4 wherein is included an infrared receiver comprising an infrared-sensitive element, a scanner, means for sweeping said scanner in a spiral pattern, an oscilloscope, and means for synchronizing the beam sweep, of said oscilloscope with the sweep of said scanner, the intensity of said oscilloscope connected to be controlled by the output of said infrared-sensitive element.

References Cited in the file of this patent UNITED STATES PATENTS Tolson Sept. 20, 1938 Becker Mar. 21, 1939 Maybarduk Nov. 12, 1946 Kell et a1. June 24, 1947 Alexanderson Oct. 17, 1950 FOREIGN PATENTS Great Britain July 25, 1946 

